1. Field of the Invention
The present invention relates to a method of marking marks on a metallic layer, and a metallic layer with marks and a semiconductor device having the metallic layer, in more detail, relates to a method of marking marks (emblem) such as characters, codes, patterns or the like by illuminating a laser beam on a surface of a metallic layer, a metallic layer with marks thereon, and a semiconductor having a metallic layer with marks thereon.
2. Description of Related Art
So far, as a method of marking marks such as characters, codes, patterns or the like on a surface of a metallic member in order to indicate product names, product specifications, logotypes, product lot numbers or the like, such as shown in FIG. 6, a laser marking method of illuminating a laser beam 2 on a surface of a metallic layer 1 is known. According to this method, the energy of the illuminated laser beam 2 sublimes metal particles or spatters metallic debris 3 from the surface of the metallic layer 1 to dig concave portions thereon, the dug portions 4 being the marking portions.
However, in the case of applying such so far employed marking method to a metallic member in which an underlying metallic layer is covered by a thin metallic plating layer, due to illumination of a laser beam 2, a part or all of the plating layer is removed. Here, since corrosion reaction such as oxidation or the like occurs due to exposure of the underlying metal, there is a problem such as deterioration of visibility occurs.
In a BGA (ball grid array) type semiconductor device having a heat-radiating cover plate, for instance, though a cover plate covered by a nickel plating layer (thickness of 2 to 10 .mu.m) is disposed on a surface of a copper plate for preventing from rusting, in the case of carrying out marking by conventional illumination of a laser beam on such a cover plate, the nickel plating layer is removed to expose the underlying copper layer, due to corrosion of copper, the visibility of the dug portions 4 is deteriorated.
Further, in the conventional method, the marking is carried out by deleting the surface of the metallic layer 1, air contaminating substances such as metallic debris 3 or metal particles are generated, accordingly measures such as dust collection or the like were necessary. Further, there is a troublesome problem such that, in order for the generated and floating metallic debris 3 or the like not to interrupt the laser beam 2, digging operation is required to be carried out while evacuating/removing these floating materials by a suction pump.